A special and important role of the mammalian hematopoietic system is to generate erythrocyte which delivers oxygen to the tissues of the animal. Lifespan determination of erythrocyte can be used for the differential diagnosis of anemia and other diseases, understanding the disease pathogenesis and determining the prognosis of treatment. Accordingly, the measurement of human erythrocyte lifespan is essential. The study has confirmed that the difference between the CO concentration of the exhaled alveolar air and the CO concentration in the base gas of the place where the sample gas of the exhaled alveolar air was taken can be used to estimate human erythrocyte lifespan. Common methods for measuring CO concentrations in air comprise non-dispersive infrared spectroscopy, gas chromatography, electrochemical methods, mercury replacement methods, etc. Among others, non-dispersive infrared spectroscopy and electrochemical methods, because of the need for large amount of gas samples, are not suitable for the CO concentration measurement of the human body breath. The amount of samples needed by gas chromatography is small, and the measurement accuracy can also satisfy with the determination of the low CO concentration in exhaled alveolar air for estimating erythrocyte lifespan. However, the operation and maintenance of the instrument are complex and expensive, so it is not suitable for clinical use. At the same time, the measured value of the existing equipment is about the CO concentration in the measuring chamber, and there is a certain deviation between this concentration and the CO concentration in exhaled alveolar air under normal conditions. The reason for this deviation is due to the mixing of the ambient air caused by the inconsistent operation during the exhaled alveolar air sampling and injecting. The existing methods and equipments cannot identify and eliminate the deviation.